Blood treatment apparatus

ABSTRACT

A blood treatment apparatus ( 1 ) comprising a degassing unit ( 15 ) receiving gas-containing fluid and supplying degassed fluid to a fluid chamber ( 3 ) of a blood treatment unit ( 2 ). The degassing unit has a gas separator ( 16 ), a degassing pump ( 18 ) to circulate fluid in a degassing line ( 12 ), a flow restrictor ( 17 ) for reducing the pressure in the degassing line ( 12 ), an absolute pressure sensor ( 19 ), and a control unit ( 20 ) designed to control the speed of said degassing pump from the absolute pressure signal emitted by the pressure sensor. The apparatus comprises a dialysis machine provided with a device for preparing on-line a dialysis liquid from water and concentrates. The apparatus achieves an accurate and reliable regulation of a desired concentration of gas in the dialysis liquid.

BACKGROUND OF THE INVENTION

The invention relates to a blood treatment apparatus, and particularlyto a blood treatment apparatus provided with a device for on-linepreparation of a treatment liquid.

Specifically, though not exclusively the invention can be usefullyapplied in a dialysis machine provided with a device for preparingon-line a dialysis liquid from water and concentrates.

As is well known, air bubbles in the dialysis liquid render inoperativethe semipermeable membrane of the dialyzer. Therefore a dialysis machinenormally includes a device for removing gas and minimizing gas in thedialysis liquid. For example, one type of gas removal system, as shownin U.S. Pat. No. 3,738,382, includes a heater for heating the water to ahigh temperature and a debubbling chamber for removing gas from theheated water at atmospheric pressure. This system does not effectivelydegass the water and the heating of the water causes dissolved mineralsto precipitate and clog passageways within the dialysis machine. Asecond type of gas removal system is shown in U.S. Pat. No. 3,528,550.In this system water is fed to a degassing chamber which is maintainedat a pressure below atmospheric pressure by a Venturi through whichdialysis solution flows. Thus the pressure in the degassing chamber isdirectly related to the dialysis solution flow rate through the Venturi.The Venturi only applies a moderately negative pressure to the degassingtank and thus does not effectively degass the water. In the degassingsystem shown in U.S. Pat. No. 3,528,550, the degassing chamber pressuremay vary with dialysis solution flow rate, which, in turn, may vary withdialysis conditions, such as patient size, etc. Variations in degassingchamber pressure may affect gas removal. During dialysis it is desirableto control the dialysis solution pressure in the dialyzer. However,changes in the dialysis solution flow rate through the dialyzer causethe dialysis solution pressure to vary.

U.S. Pat. No. 4,348,280 provides a degassing system which functionsindependently of the dialysis solution flow rates and further providesmeans for controlling the dialysis solution pressure in the dialyzer asthe dialysis solution flow rate changes. In the degassing systemproposed by U.S. Pat. No. 4,348,280 water at normal body temperature isfed to a degassing tank that is continuously subjected to a controllablehigh negative pressure. The pressure is provided by two pumps, one ofwhich draws gas from the tank and another of which draws degassed waterfrom the tank. The degassing tank pressure is thus independent of thedialysis solution flow rate. The dialysis solution pressure and flowrate at the dialyzer are controlled by a pair of flow restrictions whichare positioned one upstream and the other downstream of the dialyzer.This permits accurate control of the dialysis solution flow rate andpressure within the dialyzer.

U.S. Pat. No. 4,153,554 discloses an apparatus for delivering adialysate solution to an artificial kidney. The apparatus prepares thesolution by mixing water with a concentrated solution in a predefinedratio. The water enters a heater and then flows into a float tank whichis filled with a controlled volume of water by means of afloat-controlled valve. Air bubbles are removed from the tank by meansof a vacuum pump, which creates a partial vacuum on the float tank andpasses air out of a vent. The water is then drawn from the float tank bya supply pump and boosted back to about +5 psig pressure which ismaintained by a pressure regulator arranged downstream to the supplypump. A deaerator removes additional air from the water by passing thewater over a vertical baffle near an upper air space which is incommunication with the top of the float tank by means of a line having arestriction which is adapted to maintain the 5 psig pressure in thedeaerator and thus in the water as it leaves the deaerator. Since thesupply pump has a constant pressure of about 5 psig to work against, itis possible to maintain a steady flow of dialysate out to an artificialkidney.

The hemodialysis apparatus of U.S. Pat. No. 4,828,693 comprises meansfor removing air entrapped in the incoming water from the water streamprior to a proportioning pump. The air is removed in a deaeration looputilizing a deaerator having a float valve and air outlet. The incomingwater is fed to a deaerator pressure regulator having an outlet to thedeaerator. The deaerator outlet is connected to a pump, thence back tothe pressure regulator completing the deaeration loop. The pump createsa negative pressure in the deaerator pressure regulator, drawing theincoming water into the deaerator at which point the entrapped air inthe water escapes via the float valve and air outlet at a lower negativepressure. The deaeration pressure regulator controls the negativepressure to a selected value, for example −23 inches of mercury. Theincoming water to the deaeration pressure regulator is generallycontrolled by a first pressure regulator to 12 psig. The outlet waterfrom the deaeration pressure regulator is supplied to the proportioningpump. U.S. Pat. No. 4,828,693 adds a second regulator, termed a backpressure regulator, to receive water from the deaeration pump and tocontrol the pressure of that water to a value higher than 12 psig; forexample, 15 psig. The output from the backpressure regulator thensupplies the water to the dialysate-proportioning pump. Thus, thepressure of the water to the proportioning pump is independent of theincoming water pressure since the deaerator loop serves as a constantvolume source of water to the pump and the pump is independent of theincoming water pressure and flow.

U.S. Pat. No. 4,229,299 describes a dialysate proportioning systemprovided with deaeration means for removing soluble gases from theheated water prior to passage thereof to the proportioning means. Watercontaining desolubilized gases is passed from a heater to a first ventedtank. Partially deaerated water is removed from the first tank through aconduit into a second vented tank. The conduit has an adjustable flowrestrictor which depressurizes the liquid so as to release additionalsoluble gases therefrom. A pressure sensor is arranged downstream fromthe restrictor to permit any necessary adjustment of flow restrictor inorder to maintain a predetermined pressure level. A vacuum pump isarranged on the conduit downstream from the pressure sensor. In order toenhance removal of soluble gases, a recirculation conduit joins thefirst tank with the second tank for recirculation of a portion of thefinally deaerated water from the second tank to the first tank.

U.S. Pat. No. 5,762,782 describes a water treatment process for use in adialysate preparation machine wherein warm water is passed through awater pressure regulator past a manually operated valve. The pressureregulator supplies water to the dialysate preparation unit at asubstantially constant pressure. The water then passes through a chamberloaded with a carbon filtration agent which removes organic material anddissolved gases from the water.

WO 00/57935 describes an apparatus for the preparation of peritonealdialysis fluid wherein preheated water passes through a series ofcomponents which remove dissolved gas from the water. These componentsare a proportioning valve, a degassing restrictor, an expansion chamber,a degassing pump and a degassing chamber. In operation, water from thedegassing chamber is recirculated via the proportioning valve throughthe degassing restrictor by the degassing pump. The pressure drop in thewater due to the degassing restrictor causes dissolved gas in the waterto be forced out of solution and begin to form bubbles in the water. Thepressure drop due to the degassing restrictor is a function of the flowrate there-through, which is maintained constant by recirculation fromthe degassing chamber, at a flow rate set by the degassing pump.

The prior art includes also AK 100/200/95® dialysis machines (producedby Gambro®) each of which comprises a blood treatment apparatus as inthe preamble of claim 1.

SUMMARY OF THE INVENTION

A main aim of the present invention is to effectively remove gasbubbles, especially air bubbles, from the entire circulatory system of ablood treatment apparatus thereby to increase the efficiency of thetreatment (e.g. dialyzing) operation.

An advantage of the invention is to provide an economical and efficientdegassing system for use in a blood treatment apparatus.

A further advantage of the invention is to provide a pump-type degassingsystem for use in a blood treatment apparatus in which degasification iseffectively and efficiently achieved also when the performances of thedegassing pump are reduced.

A further advantage is to enable a desired concentration of gas (neithertoo high nor too low) in the treatment liquid to be accurately andreliably regulated.

A further advantage is to provide a device for preparation of atreatment liquid provided with a pressure reducer arranged at the inletof the hydraulic circuit in which there is no need to calibrate thepressure reducer when the device is installed at different altitudes.

Another advantage of the invention is that it provides a device forremoving gases, which will enable a high separation rate to be attainedwith a compact and simple type of construction.

A further advantage of this invention is that it provides a pump-typedegassing system for use in a blood treatment apparatus which isflexible in that it is adaptable for use under varying conditions and inwhich the relationship between degassing and other conditions (altitude,dialysis liquid flow rate, dialyzing liquid pressure, pump performances,etc.) will not undesirably change during operation.

A further advantage of the invention consists in the fact that theefficiency of the degassing pump can be maximized by appropriatelyselecting the degassing pressure set point.

These aims and advantages and more besides, which will better emergefrom the description that follows, are attained by a blood treatmentapparatus according to one or more of the accompanying claims.

Further characteristics and advantages of the present invention willbetter emerge from the detailed description that follows, of at least apreferred embodiment of the invention, illustrated by way ofnon-limiting example in the accompanying figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will follow herein below, with reference to the figuresof the drawings, provided as a non-limiting example and in which:

FIG. 1 is a schematic diagram of a blood treatment apparatus accordingto a first embodiment of the present invention;

FIG. 2 is a schematic diagram of a blood treatment apparatus accordingto a second embodiment of the present invention.

DETAILED DESCRIPTION

With reference to the above-cited FIG. 1 of the drawings, 1 denotes inits entirety a blood treatment apparatus, particularly a hemodialysis orhemo(dia)filtration apparatus.

The blood treatment apparatus 1 comprises a blood treatment unit(hemodialyser or hemo(dia)filter) 2 having a fluid chamber 3, a bloodchamber 4, and a semipermeable membrane 5 separating the fluid chamber 3from the blood chamber 4.

An extracorporeal blood circuit connects a patient vascular access 6with the blood chamber 4. The extracorporeal blood circuit comprises anarterial line 7 for transporting the blood to be treated from thevascular access 6 to an inlet of the blood compartment 4, and a venousline 8 for returning the treated blood to the vascular access 6. Theextracorporeal blood circuit can be any extracorporeal blood circuitused during a blood treatment in the prior art.

The blood treatment apparatus 1 comprises a treatment fluid supply line9 comprising a water inlet connected to a water source 10, and atreatment fluid outlet connected to the fluid chamber 3 (hemodialysistreatment) and/or to the extracorporeal blood circuit(hemodiafiltration/hemofiltration treatment), in particular to thearterial line 7 and/or to the venous line 8 (pre- and/or post-dilution).

The blood treatment apparatus 1 comprises a preparation device 11connected to the treatment fluid supply line 9 to prepare the treatmentfluid from water and concentrates. In this specific case the treatmentfluid is a dialysis fluid (dialysate) which can be used to form asubstitution fluid for hemo(dia)filtration treatments.

The blood treatment apparatus 1 further comprises a degassing line 12having an inlet 13 for receiving gas-containing fluid coming from thewater inlet, and an outlet 14 for supplying degassed fluid to thetreatment fluid outlet. In the present embodiment the treatment fluidsupply line 9 has a first junction point, which in this specific casecoincides with the inlet 13 of the degassing line 12 and from which thedegassing line 12 branches off, and a second junction point, which inthis specific case coincides with the outlet 14 of the degassing line 12and into which the degassing line 12 flows into. In the presentembodiment the preparation device 11 is located between the water inletand the gas-containing fluid inlet 13; in another embodiment (notillustrated) the preparation device 11 is located between the degassedfluid outlet 14 and the treatment fluid outlet.

A degassing unit 15 is operatively connected to the degassing line 12.the degassing unit 15 comprises a gas separator 16 for separating thegas in the gas-containing fluid flowing in the degassing line 12, a flowrestrictor 17 for reducing the pressure of the fluid flowing in thedegassing line 12, a degassing pump 18 for circulating the fluid in thedegassing line 12, a pressure sensor 19 for emitting a pressure signalindicative of the pressure in the degassing line 12, and a control unit20 designed to control the speed of the degassing pump 18 on the basisof the pressure signal emitted by the pressure sensor 19.

In the present embodiment the gas separator 16 comprises a gasseparation chamber. The signal used by the control unit 20 to controlthe degassing pump 18 is one that indicates the absolute pressure in thedegassing line 12. In the present embodiment the pressure sensor 19 isan absolute pressure sensor designed to emit an absolute pressuresignal. The degassing pump 18 has a delivering outlet connected to afluid inlet of the gas separator 16. The degassing pump 18 is located inthe degassing line 12 between the restrictor 17 and the gas separator16. The degassing pump 18 is located in the degassing line 12 betweenthe pressure sensor 19 and the gas separator 16. The pressure sensor 19is located in the degassing line 12 between the restrictor 17 and thegas separator 16. The pressure sensor 19 is located in the degassingline 12 between the restrictor 17 and the degassing pump 18. In thisspecific case the degassing pump 18 is a positive displacement pump(e.g. a gear pump).

The blood treatment apparatus 1 further comprises a discharge line 21connecting the fluid chamber 3 with a drain. The gas separator 16comprises a gas outlet connected through a vent line 22 to the dischargeline 21. The vent line 22 is provided with a closing valve 23 controlledby the control unit 20.

A one-way valve 24 is arranged in the treatment fluid supply line 9between the first junction point (inlet 13) and the second junctionpoint (outlet 14) so as to block the flow from the inlet 13 to theoutlet 14.

During operation the dialysate flow rate in the degassing line 12 shouldbe higher than (e.g. twice as high as) the flow rate in the treatmentfluid supply line 9. The fluid (in this case dialysate) which enters theinlet 13 contains air bubbles and dissolved air. To reduce air in thefluid, the fluid is forced to pass through the deaeration restrictor 17.The speed of the pump 18 is controlled from the pressure, in particularthe absolute pressure, in the degassing line 12. In this specific casethe pump speed is controlled in a closed loop on the basis of thepressure signal emitted by the pressure sensor 19. In particular thedegassing pump 18 controls the pressure in the degassing line 12 at aconstant absolute pressure (e.g. 100 mmHg) set to achieve a desireddegassing effect, particularly a desired percentage of gas in thetreatment fluid. In this way the desired amount of gas in the treatmentfluid is always achieved under varying conditions (decrease inefficiency of the degassing pump 18, narrowing of the restrictor 17,difference in altitude, etc.).

The removed air is collected in the gas separator (chamber) 16 andperiodically vented to the drain. In this case the liquid level in theseparation chamber is monitored by a level sensor (not shown). When thelevel sensor detects air in the chamber, the valve 23 is opened to ventthe accumulated air. The valve 23 is closed when the level sensordetects liquid again.

We will refer now to FIG. 2 which shows a second embodiment according tothe invention. The numbering of FIG. 1 has been maintained also in FIG.2 for analogous elements.

The blood treatment apparatus (hemodialysis or hemo(dia)filtrationapparatus) of FIG. 2 comprises a blood treatment unit (hemodialyser orhemo(dia)filter) 2 having a fluid chamber 3, a blood chamber 4, and asemipermeable membrane 5 separating the fluid chamber 3 from the bloodchamber 4.

An extracorporeal blood circuit connects a patient vascular access (notshown) with the blood chamber 4. The extracorporeal blood circuitcomprises an arterial line 7 and a venous line 8.

The blood treatment apparatus 1 comprises a treatment fluid supply line9 having a water inlet connected to a water source 10, and a treatmentfluid outlet connected to the fluid chamber 3 (hemodialysis treatment)and/or to the arterial line 7 and/or to the venous line 8(hemodiafiltration/hemofiltration treatment with pre- and/orpost-dilution).

The blood treatment apparatus 1 comprises a preparation device 11connected to the treatment fluid supply line 9 to prepare the treatmentfluid from water and concentrates. In this specific case the treatmentfluid is a dialysis fluid (dialysate) which can be used to form asubstitution fluid for hemo(dia)filtration treatments. The treatmentfluid preparation device 11 can comprise a central delivery systemconnected to the blood treatment apparatus 1, or a device for preparinga fluid from water and concentrates.

The blood treatment apparatus 1 further comprises a degassing line 12having an inlet 13 to receive gas-containing fluid coming from the waterinlet, and an outlet 14 for supplying degassed fluid to the treatmentfluid outlet. In this specific case the treatment fluid supply line 12has a first junction point, which in this specific case coincides withthe inlet 13 of the degassing line 12 and from which the degassing line12 branches off, and a second junction point, which in this specificcase coincides with the outlet 14 of the degassing line 12 and intowhich the degassing line 12 flows. In this specific case the preparationdevice 11 is located between the degassed fluid outlet 14 and thetreatment fluid outlet.

A degassing unit 15 is operatively connected to the degassing line 12.The degassing unit 15 comprises a gas separator 16 for separating thegas in the gas-containing fluid flowing in the degassing line 12, a flowrestrictor 17 for reducing the pressure of the fluid flowing in thedegassing line 12, a degassing pump 18 for circulating the fluid in thedegassing line 12, a pressure sensor 19 for emitting a pressure signalindicative of the pressure in the degassing line 12, and a control unit20 designed to control the speed of the degassing pump 18 on the basisof the pressure signal emitted by the pressure sensor 19.

In the present embodiment the gas separator 16 comprises a gasseparation chamber. The signal used by the control unit 20 to controlthe degassing pump 18 is a signal indicative of the absolute pressure inthe degassing line 12. In this specific case the pressure sensor 19 isan absolute pressure sensor designed to emit an absolute pressuresignal. The degassing pump 18 has a delivering outlet connected to afluid inlet of the gas separator 16. The degassing pump 18 is located inthe degassing line 12 between the restrictor 17 and the gas separator16. The degassing pump 18 is located in the degassing line 12 betweenthe pressure sensor 19 and the gas separator 16. The pressure sensor 19is located in the degassing line 12 between the restrictor 17 and thegas separator 16. The pressure sensor 19 is located in the degassingline 12 between the restrictor 17 and the degassing pump 18. In thepresent embodiment the degassing pump 18 is a positive displacement pump(e.g. a gear pump).

The blood treatment apparatus 1 further comprises a discharge line 21connecting the fluid chamber 3 with a drain. The gas separator 16comprises a gas outlet connected through a vent line 22 to the drain.The vent line 22 can be connected to the discharge line 21. The ventline 22 is provided with a closing valve 23 controlled by the controlunit 20.

A one-way valve 24 is arranged in the treatment fluid supply line 9between the first junction point (inlet 13) and the second junctionpoint (outlet 14) so as to block the flow from the inlet 13 to theoutlet 14.

The apparatus of FIG. 2 further comprises a pressure reductor 25arranged immediately after the water inlet to control the pressure byrestricting the fluid passage. A normally closed inlet valve 26 islocated downstream the pressure reductor 25. The apparatus of FIG. 2comprises a first ultrafilter 27 designed to retain bacteria orendotoxin. The first ultrafilter has a first chamber (retentate chamber)separated from a second chamber (permeate chamber) by a semipermeablemembrane. A flushing line 28 connects an outlet of the first chamber ofthe first ultrafilter with the drain. An orifice 29 is arranged in theflushing line 28 to limit the flow rate of fluid flushed through thefirst chamber and the flushing line 28 and then into the drain. A checkvalve 30 prevents a back-flow coming from the drain polluting the firstultrafilter 27.

A heater 31 is arranged in the degassing line 12 upstream the restrictor17 to heat the incoming fluid. A temperature sensor 32 measures thetemperature of the fluid in the degassing line 12 (downstream of theheater 31). The control unit 20 controls the heater 31 to ensure thatthe temperature measured by the sensor 32 is within a desired range. Aflow switch 33 is arranged in the degassing line 12. The control unit 20recognizes an alarm situation (and disconnects the power from the heater31, for example) when the flow rate through the flow switch 33 is lowerthan a predetermined value. In another embodiment (not shown) the heater31 is located downstream of the restrictor 17, e.g. between therestrictor 17 and the degassing pump 18, or between the restrictor 17and the pressure sensor 19.

A restrictor bypass valve 34 is arranged in a bypass line connected tothe degassing line 12, for bypassing the restrictor 17. The restrictorbypass valve 34, which is normally closed, is opened during a heatdisinfection procedure—which serves to disinfect the hydraulic circuitof the blood treatment apparatus—and is closed during a blood treatmentprocedure. When the restrictor bypass valve 34 is opened during a heatdisinfection procedure, the degassing restrictor 17 is bypassed in orderto prevent the heated liquid (water) from boiling.

A pressure regulator 35 is arranged in the treatment fluid supply line 9between the degassing line 12 and a supply pump 36 circulating a fluidin the treatment fluid supply line 9. The pressure regulator 35 isarranged downstream of the degassing line 12. The pressure regulator 35is set to maintain a desired pressure in the concentrate sources 37 aand 37 b. When the concentrate sources comprise cartridges of dryconcentrates a moderate overpressure inside the cartridges can bedesirable. The pressure regulator 35 avoids a too-low pressure causingthe formation of gas bubbles upstream of the supply pump 36. Moreoverthe pressure regulator 35 prevents or reduces pressure spikes comingfrom the gas separator 16 (gas separation chamber or bubble trap) duringthe above-described gas evacuation.

The treatment fluid (dialysate) preparation device 11 comprises at leasttwo injection lines each operatively associated to a concentrate source37 a and 37 b (liquid or solid concentrates), to a dosing pump 38 a and38 b, and to a conductivity sensor 39 a and 39 b controlling arespective dosing pump to a set conductivity value. The injection linesare supplied with a solvent (e.g. water) from a line branching off fromthe treatment fluid supply line 9.

The apparatus of FIG. 2 comprises a second ultrafilter 40 designed toretain bacteria or endotoxin. The second ultrafilter 40 has a firstchamber (retentate chamber) separated from a second chamber (permeatechamber) by a semipermeable membrane. A flushing line 41 connects anoutlet of the first chamber of the second ultrafilter 40 with thedischarge line 21. The flushing line 41 is provided with a flushingvalve 42 which is periodically (or under predetermined conditions)opened to tangentially flush the second ultrafilter 40.

A first bypass line 43 is arranged upstream of the second ultrafilter 40to connect the supply line 9 with the discharge line 21. The firstbypass line 43 is provided with a first bypass valve 44. A second bypassline 45 is arranged downstream of the second ultrafilter 40 to connectthe supply line 9 with the discharge line 21. The second bypass line 45is provided with a second bypass valve 46. A closing valve 47 isarranged in the discharge line 21 before the second bypass line 45. Adischarge pump 48 is arranged downstream of the flushing line 41. Thedischarge pump 48 is arranged downstream of the first and second bypasslines 43 and 45. The discharge pump 48 circulates the fluid towards thedrain. A fluid balance system controls the discharge pump 48 (and thesupply pump 36) to regulate the weight loss of a patient undergoing ablood treatment. In this specific case the fluid balance systemcomprises an upstream flowmeter 49 arranged before the blood treatmentunit 2 in the supply line 9, and a downstream flowmeter 50 arrangedafter the blood treatment unit 2 in the discharge line 21.

The control unit 20 is designed to control the degassing pump 18 (duringthe treatment) at a flow rate which is greater than that of thetreatment fluid supply pump 36. During the treatment the valve 34 isclosed and the fluid (water) is passed through the degassing restrictor17. The degassing system of the FIG. 2 apparatus operates as abovedescribed in order to reduce gas in the fluid.

The control unit 20 is designed to control the degassing pump 18 at apredetermined degassing pressure set point.

The degassing pressure can be set as low as possible in order tomaximize the degassing performance, i.e. the removal of oxygen. However,there are some limitations as to how low the degassing pressure can beset. For example, a too-low degassing pressure may result in cavitationin the pump causing increased wear and/or a loss of pump efficiency.

The selection of the degassing set point may be a trade-off betweendegassing performance and other requirements such as, e.g., pump life,cost and power consumption.

In a further embodiment (not shown) a blood treatment apparatus differsfrom the apparatus of FIG. 1 (or FIG. 2) only in that the pressuresignal that indicates the absolute pressure in the degassing line 12 maybe supplied by processing two pressure signals emitted by a firstrelative pressure sensor arranged in the degassing line 12 (at the samelocation of the absolute pressure sensor 19) and a second pressuresensor indicating the atmospheric pressure. A calculation unit maycalculate an absolute pressure value from said two pressure signals,e.g. as a difference between the pressure values indicated by the twopressure signals. The control unit 20 may include the calculation unit.

In a further embodiment (not shown) a blood treatment apparatus differsfrom the apparatus of FIG. 1 (or FIG. 2) only in that the degassing lineforms a tract (initial, intermediate, or final tract) of the treatmentfluid supply line without forming a loop between two junction pointsthereof. In this embodiment the degassing line and the treatment fluidsupply line form a continuous fluid line, whereby the flow rate of thedegassing line is equal to the flow rate of the treatment fluid supplyline and the supply pump of the treatment fluid supply line may act asdegassing pump of the degassing line.

LEGEND

-   -   1 Blood treatment apparatus    -   2 Blood treatment unit    -   3 Fluid chamber    -   4 Blood chamber    -   5 Semipermeable membrane    -   6 Patient vascular access    -   7 Arterial line    -   8 Venous line    -   9 Treatment fluid supply line    -   10 Water source    -   11 Treatment fluid preparation device    -   12 Degassing line    -   13 Inlet of degassing line    -   14 Outlet of degassing line    -   15 Degassing unit    -   16 Gas separator    -   17 Flow restrictor    -   18 Degassing pump    -   19 Pressure sensor    -   20 Control unit    -   21 Discharge line    -   22 Vent line    -   23 Closing valve    -   24 One-way valve    -   25 Pressure reductor    -   26 Inlet valve    -   27 First ultrafilter    -   28 Flushing line    -   29 Orifice    -   30 Check valve    -   31 Heater    -   32 Temperature sensor    -   33 Flow switch    -   34 Restrictor bypass valve    -   35 Pressure regulator    -   36 Supply pump    -   37 Concentrate sources (37 a, 37 b)    -   38 Dosing pumps (38 a, 38 b)    -   39 Conductivity sensors (39 a, 39 b)    -   40 Second ultrafilter    -   41 Flushing line    -   42 Flushing valve    -   43 First bypass line    -   44 First bypass valve    -   45 Second bypass line    -   46 Second bypass valve    -   47 Closing valve    -   48 Discharge pump    -   49 Upstream flowmeter    -   50 Downstream flowmeter

1-24. (canceled)
 25. A blood treatment apparatus comprising: a bloodtreatment unit having a fluid chamber, a blood chamber, and asemipermeable membrane separating the fluid chamber from the bloodchamber; an extracorporeal blood circuit connecting a patient vascularaccess with said blood chamber; a treatment fluid supply line comprisinga gas-containing fluid inlet connected to a gas-containing fluid source,and a treatment fluid outlet connected to said fluid chamber and/or tosaid extracorporeal blood circuit; a degassing line having a degassingline inlet for receiving gas-containing fluid coming from saidgas-containing fluid inlet, and a degassing line outlet for supplyingdegassed fluid to said treatment fluid outlet; a degassing unitoperatively connected to said degassing line, said degassing unitcomprising: a degassing pump for flowing the fluid in said degassingline from said degassing line inlet to said degassing line outlet, a gasseparator for separating the gas in the gas-containing fluid flowing insaid degassing line, and a flow restrictor for reducing the pressure ofthe fluid flowing in said degassing line, wherein said apparatus furthercomprises: an absolute pressure sensor means for emitting an absolutepressure signal indicative of an absolute pressure in said degassingline, and a control unit programmed to control the speed of saiddegassing pump from said absolute pressure signal.
 26. The apparatus ofclaim 25, wherein said absolute pressure sensor means comprises anabsolute pressure sensor.
 27. The apparatus of claim 25, comprising adischarge line connecting the fluid chamber with a drain.
 28. Theapparatus of claim 27, wherein the gas separator comprises a gas outletconnected through a vent line to the discharge line.
 29. The apparatusof claim 25, wherein the degassing pump has a delivering outletconnected to a fluid inlet of the gas separator.
 30. The apparatus ofclaim 25, comprising a heater located in the degassing line for heatingthe fluid flowing in the degassing line.
 31. The apparatus of claim 30,wherein said flow restrictor is located in the degassing line betweenthe heater and the gas separator or the degassing pump.
 32. Theapparatus of claim 30, wherein said heater is located in the degassingline between said flow restrictor and said degassing pump or saidabsolute pressure sensor means.
 33. The apparatus of claim 30, whereinsaid heater is located in the degassing line downstream of said flowrestrictor.
 34. The apparatus of claim 30, wherein said heater islocated in the degassing line downstream of said absolute pressuresensor means.
 35. The apparatus of claim 25, wherein the degassing pumpis located in the degassing line between the flow restrictor and the gasseparator.
 36. The apparatus of claim 25, wherein the degassing pump islocated in the degassing line between the absolute pressure sensor meansand the gas separator.
 37. The apparatus of claim 25, wherein theabsolute pressure sensor means are located in the degassing line betweenthe flow restrictor and the gas separator.
 38. The apparatus of claim25, wherein the absolute pressure sensor means are located in thedegassing line between the flow restrictor and the degassing pump. 39.The apparatus of claim 25, wherein the absolute pressure sensor meansare located in the degassing line downstream of the flow restrictor. 40.The apparatus of claim 25, further comprising a treatment fluidpreparation device connected to said treatment fluid supply line toprepare the treatment fluid from water and concentrates.
 41. Theapparatus of claim 40, wherein the treatment fluid preparation device islocated between said degassing line outlet and said treatment fluidoutlet.
 42. The apparatus of claim 25, wherein the treatment fluidsupply line has a first junction point and a second junction point, thedegassing line forming a loop between the first junction point and thesecond junction point.
 43. The apparatus of claim 42, wherein a one-wayvalve is arranged in the treatment fluid supply line between said firstjunction point and said second junction point.
 44. The apparatus ofclaim 25, comprising a treatment fluid supply pump for displacing fluidthrough the treatment supply line.
 45. The apparatus of claim 44,wherein said treatment fluid supply pump is arranged in said treatmentsupply line.
 46. The apparatus of claim 44, wherein said control unit isprogrammed to control said treatment fluid supply pump to flow fluidthrough the treatment supply line at a first flow rate and to controlsaid degassing pump to flow fluid through the degassing line at a secondflow rate, said first flow rate being lower than said second flow rate.47. The apparatus of claim 25, wherein said gas separator comprises agas separation chamber.
 48. The apparatus of claim 25, wherein saidabsolute pressure sensor means comprises a first pressure sensor foremitting a first pressure signal indicative of a relative pressure insaid degassing line, a second pressure sensor for emitting a secondpressure signal indicative of the atmospheric pressure, and acalculation unit programmed to calculate an absolute pressure value fromsaid first and second pressure signals.